Much of the prior art in beam steering and control is for electromagnetic radiation. Thus much of the following prior art is for beam steering in optical systems. In particular, the electronic control of the direction of propagation of light, which also includes concentration, focusing and the spectral and/or spatial distribution of electromagnetic radiation in general, is often desired to enable various optical functions. For example, prior art systems have achieved some capability in beam steering by severely limiting one or more parameters, such as: wavelength, steering angle, polarization, input/output aperture extent and the angular resolution of the light steering. There are many examples of prior art that explicitly demonstrate the dynamic control of light, but with one or more shortcomings. Several such devices are now discussed and many more are available in the literature especially for narrow-band phased array systems for electromagnetic waves and sound waves.
U.S. Pat. No. 7,924,495, entitled “Active Matrix Sun Tracker”, issued to Leo DiDomenico on 2011 Apr. 11. This patent shows miniature optical elements controlled by quasi electrostatic forces. However, mechanical optical systems often require many components in a complex arrangement, are prone to wear and are potentially too costly for some applications.
U.S. Pat. No. 6,958,868 entitled “Motion-Free Tracking Solar Concentrator”, issued to John George Pender on 2005 Oct. 25. This patent shows liquid crystal filled prism arrays that can steer light. This prior art has a limited range of angles over which it can steer light due to the limited range of refractive indices that a liquid crystal can provide. It is also polarization dependent, which can only be overcome by utilizing multiple layers to compensate for polarization diversity of incident light.
U.S. Pat. No. 8,311,372 entitled “Liquid Crystal Waveguide Having Refractive Shapes For Dynamically Controlling Light”, issued to Michael H. Anderson et. al. on 2012 Nov. 13. This patent shows how to use evanescent field coupling to liquid crystals to steer light. It has shortcomings of requiring narrowband laser light having only one polarization on a predominantly two dimensional structure so that the area extent of both input and output is limited.
U.S. Pat. No. 7,215,472 entitled “Wide-Angle Beam Steering System”, issued to Irl W. Smith et. al. from Raytheon on 2007 May 8. Through the use of multiple stacked holograms a set of discrete steering angles can be addressed by means of a separate beam steerer, which selects a particular volume phase hologram within the stack of volume phase holograms to use for course steering. A second post-steering (or vernier) technology is also required to fine tune the direction of propagation of the light. One shortcoming of this invention is limited steering range, which was stated to be about ±π/4 radians. The prior art's has a total of π/2 radians for its angular field of regard for in-plane light steering and this falls significantly short of π radians needed for many applications. For systems not restricted to control radiation in a plane the typically desired solid-angle field of regard is 2π steradians, which is also not achieve by this prior art. Yet another limitation of this prior art is that it is a narrowband device that ideally functions on laser light of only one polarization.
U.S. patent application 2012/0188467 entitled “Beam steering devices including stacked liquid crystal polarization gratings and related methods of operation”, issued to Michael J. Escuti et. al. on 2012 Jul. 26. This patent shows stacks of polarization holograms formed from electronically controlled liquid crystals. Its first shortcoming is that light steering is limited to discrete angles instead of a continuous range of angles unless yet another steering technology is utilized to compensate. Another shortcoming is that the number of stages within the beam-steering stack limits the overall efficiency, which is strongly affected by: scatter, absorption, and Fresnel loss—which could be significant. Another shortcoming is that as a diffractive-based system additional layers of compensation are needed to steer different wavelengths into the same angular direction. Each of the additional layers requires a lossy transparent conductor further limiting its overall efficiency. Another shortcoming is a restricted angular field of regard, which is shown to be about ±π/4 radians in a principle plane, instead of ±π/2 radians or more. By stacking steering systems in two orthogonal directions up to 87% efficiency over an π/2×π/4 steering field of regard is possible, with with 1/45 of a radian steering increments at one wavelength of light. Larger spectral bandwidths would further increase losses. Yet another shortcoming, is that the incident light must be circularly polarized. This means that even through the polarization gratings are inherently very low loss, there is nonetheless at least a loss of 50% of any incident natural light (sunlight or light from a thermal source), which is wasted in a process used to convert the light to the correct polarization before being steered. While polarization gratings can in principle provide a means to convert natural light to circular polarized light at a normal incident angle, there is at this time no way to also provide for that polarization conversion over a large ±π/2 radian angular field of regard. Thus this light steering system is not efficient with broadband polarization-diverse natural light sources such as sunlight.
U.S. Pat. No. 7,898,740 entitled “Tunable Optical Array Device Comprising Liquid Cells”, issued to Jason Heikenfeld at. al. on 2011 Mar. 1. This patent shows an array of liquid-filled cells comprising at least two transparent and non-miscible fluids, each having a different refractive index. Voltages applied to the cells induce polarization charges that change the wetting angle of the boundary between the two non-miscible fluids, by a process called electrowetting, and this causes the optical boundary to change orientation so that light is refracted into different directions. Its shortcomings include a limited range of steering angles due to the small differences in the refractive indices of the non-miscible fluids and a relatively large light loss due to unused area surrounding each of the cells.
U.S. patent application 2010/0033788 entitled “Micromirror and Fabrication Method for Producing Micromirror”, issued to Huikai Xie et. al. on 2010 Feb. 11. This patent shows arrays of micro-mirror structures comprising a flat mirror, a pillar structure and electrothermal actuators for steering light by means of reflection. Some of its shortcomings include that fact that it is limited to reflection only and that the space surrounding each mirror is unused so that significant optical losses are possible.
The following patents describe optical switches: U.S. Pat. No. 4,988,157 entitled “Optical Switch Using Bubbles”, issued to J. L. Jackel et. al. on 1991 Jan. 29; U.S. Pat. No. 5,699,462 entitled “Total Internal Switches Employing Thermal Activation”, issued to J. E. Fouquet et. al. on 1907 Dec. 16; U.S. Pat. No. 6,707,592 entitled “Optical Switch With Static Bubble”, issued to D. W. Schroeder on 2004 Mar. 16; U.S. Pat. No. 7,024,062 entitled “Optical Switch With Low Pressure Bubble”, issued to J. J. Uebbing on 2006 Apr. 4, which all show the use of index matching fluids for switching light into typically two directions per switch by total internal reflection between input and output waveguides. Thus there is a highly restrictive requirement of having input and output waveguides to control the waves.
The shortcomings of a number of these and other prior-art systems are discussed in: “A Review of Phased Array Steering for Narrow-Band Electrooptical Systems”, By Paul F. McManamon et. al. in the Proceedings of the IEEE, vol. 97, No. 6, June 2009, which is included herein in its entirety by reference.
The “Handbook of Optofluidics”, edited by A. R. Hawkins et. al., CRC Press 2010, ISBN 978-1-4200-9354-4, provides a review of optofluidic switches based on total internal reflection from a number of different authors in section 10.1.1.1 of the handbook, the description and references of which are included in its entirety herein. The handbook goes on to describe how certain of its listed references have developed opto-fluidic switches which are restricted by the need for input and output waveguides.
The “Handbook of Optofluidics”, edited by A. R. Hawkins et. al., CRC Press 2010, ISBN 978-1-4200-9354-4, provides a review of optofluidic deflectors and beam scanners from many authors in section 10.1.1.3 of the handbook, the description and references of which are included in its entirety herein. The handbook goes on to describe electrowetting micro-prisms as well as micro-mirrors mounted on membranes that are actuated by means of a pressure differential. These techniques are limited in area coverage or steering angle range as described in the handbook.
The “Handbook of Optical and Laser Scanning”, edited by Gerald F. Marshall, ISBN: 0-8247-5569-3, which is an authoritative review of methods of optical and laser scanning describes the shortcomings of current light steering technologies.
Therefore, it is clear that there are many methods for steering light (and by extrapolation other forms of wave energy) and that these methods have an assortment of shortcomings. Moreover, there is a clear need for a method of steering light that can overcome the shortcomings cited above.